(a) Field of the Invention
A negative active material for rechargeable lithium battery, a method for preparing a negative active material for a rechargeable lithium battery, and a rechargeable lithium battery including the same are disclosed.
(b) Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as a power source for small portable electronic devices. The lithium rechargeable batteries use an organic electrolyte solution and thereby have twice as high a discharge voltage as a conventional battery using an alkali aqueous solution, and accordingly, have high energy density.
As for a positive active material for a lithium rechargeable battery, a lithium-transition metal oxide being capable of intercalating lithium such as LiCoO2, LiMn2O4, LiNi1-xCoxO2 (0<x<1), and the like has been used.
As for a negative active material for a lithium rechargeable battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon capable of intercalating and deintercalating lithium ions have been used.
Since graphite among the carbon-based materials has a low discharge potential relative to lithium of about −0.2 V, a battery using the graphite as a negative active material has a high discharge potential of about 3.6 V and excellent energy density.
Furthermore, the graphite guarantees a long cycle life for a battery due to its outstanding reversibility. However, a graphite active material has a low density and consequently a low capacity (theoretical density: about 2.2 g/cc) in terms of energy density per unit volume when using the graphite as a negative active material.
Further, a battery may be swelled and thus have decreased capacity, because graphite is likely to react with an organic electrolyte at a high discharge voltage.
In order to solve these problems, a great deal of research on an oxide negative active material such as silicon, tin, and the like has recently been performed.
A silicon-based negative active material has an advantage of realizing high capacity when it reacts with lithium ions but problems of weak contact with a current collector and deteriorating capacity due to a volume change of greater than or equal to about 300% during charge and discharge.
In addition, silicon has low electrical conductivity and no smooth charge transfer reaction when intercalating/deintercalating lithium.
In order to solve the problems, a great deal of research has been made, and in particular, research on coating a material that does not react with carbon or lithium on the surface of silicon is actively being made.